The present invention relates to an automatic tension regulating device for a remote control wire (hereinafter referred to as "tension regulating device"), and, more particularly, to a device which can automatically eliminate permanent elongation and excessive tension during operation of the wire, when the permanent elongation or excessive tension occurs in the remote control wire, whereby the tension of the wire is regulated so that the most suitable tension is normally applied to the wire.
Conventionally, a pull wire, a push-pull wire or an inner wire of a control cable (in this specification, those wires are generally referred to as "wire") has been widely used as a means for remotely controlling a clutch device or a brake device in an automobile, or the like. The wire usually comprises a strand of steel cords, synthetic resin cords, or the like.
The above-mentioned wire has an end connected to a driven member resiliently urged in the return direction by a return spring in a driven apparatus such as a clutch device or a brake device, and has another end connected to an operating means such as a clutch pedal or a hand lever. In general, the middle portion of the wire is guided with a set of pulleys rotatably mounted on a static member, for example, a frame or body of an automobile in order to change the path of the wire. Further, a wire is slidably inserted into a conduit and has both ends fixed to the above-mentioned static member. The mechanism is known as a control cable or Bowden cable. In the remote control mechanism arranged as mentioned above, when a wire-operating means is operated to pull the end of the wire, the motion is transmitted to the driven apparatus such as the clutch device through the wire. Therefore, the driven member in the driven apparatus is operated to be pulled against the urging force of the return spring. When the operational force pulling the wire is released, the driven member returns to an original position or return-point.
On the other hand, since the wire comprising a strand of steel cords or the like receives a repeated tension-and-relaxation operation over a long period, a permanent elongation gradually occurs in the wire. Therefore, the wire is loosened and the operational force cannot be accurately transmitted to the driven side.
In order to absorb such a permanent elongation of the wire, hitherto, various methods have been proposed. For example, a mechanism in which the wire is separated in a medium and two relatively rotatable pulleys are provided for winding each end of the separated wire has been known. In such a mechanism, when slack, due to permanent elongation, occurs in the wire, the pulleys are relatively shifted to rotate, and then, they are joined together, in order to directly adjust the effective length of the wire. Further, when the above-mentioned control cable is used, the effective length of the inner wire is usually indirectly adjusted by screwing an end-fitting of the conduit to linearly move them in the wire-extending direction in order to shorten or enlarge the length of the conduit.
In the above-mentioned devices, absorbing the elongation must be manually performed every time the elongation occurs in the wire. Therefore, if the above-mentioned general method is employed, the effort needed to absorb the elongation becomes very troublesome. In order to resolve such a problem, for example, Japanese Unexamined Utility Model Publications No. 79268/1976 and No. 21358/1977 disclose devices for automatically absorbing an elongation of a wire during the operation of the wire.
The conventional device is a means for absorbing the elongation of the wire with a one-way-clutch means having ratchet teeth and a pawl. That is to say, the conventional automatic elongation-absorbing device is constructed on the assumption that the wire is only gradually elongated, and it is not necessary to make the wire longer.
An elongation of the wire includes not only the above-mentioned permanent elongation, but also an elastic elongation which temporarily occurs in the wire only when the wire receives an external force, and returns to an original form after the external force is eliminated. Furthermore, an apparent elongation or slack occurs in the wire when a frame, or the like, along which the wire is arranged, is elastically deformed. Those elastic elongation and apparent elongation must not be absorbed since excessive tension occurs in the wire if the elastic or apparent elongation is eliminated. However, the above-mentioned conventional automatic elongation-absorbing device disadvantageously absorbs not only the permanent elongation, but also the elastic or apparent elongation in the wire, since the devices absorbs all generated elongation without distinction of the cause thereof. Further, excessive tension which occurs in the wire, for example, by absorbing the elastic elongation, cannot be automatically eliminated. For example, when one of the above-mentioned automatic elongation-absorbing devices is applied to a control cable for a clutch-operating device in an automobile, the device absorbs an apparent elongation of the wire due to deformation of a chassis or a body of the automobile during operation of the vehicle. Also, the device absorbs an elastic elongation of the wire due to an overload applied to the inner wire during manual operation, and the like.
As a result, excessive tension occurs in the inner wire, and further, two clutch plates opposited to each other are always incompletely engaged with each other, and therefore, the clutch plates will burn due to friction. Further, when one of the devices is applied to a control cable used in a brake device, the brake device always acts due to the above-described excessive tension, so that the brake linings will burn.
On the other hand, after the clutch plate of the clutch device or the brake lining of the brake device is gradually worn away, since the effective length of the wire becomes insufficient, excessive tension is applied to the inner wire, for example, when a clutch pedal is operated. Therefore, it is necessary to adjust the length of the inner wire to make it longer.
With respect to an automatic tension regulating devices which can automatically lengthen the wire to eliminate excessive tension in the wire, for example, No. EP-A-120616, U.S. Pat. No. 4543849 and WO No. 84/01196 have disclosed several devices.
However, the above-mentioned devices are for adjusting tension of a control wire by adjusting an effective length of a conduit of a control cable, and therefore, they cannot be applied to a device in which only a control wire is used without a conduit. Further, in the above-mentioned conventional devices, an adjusting spring makes the effective length of the conduit long, i.e. to shorten the effective length of the inner wire when the operating means returns to the original position. Therefore, an urging force of the adjusting spring cannot be offset or balanced with the reversely urging force of the return spring for the operating means itself since there is no connection between the adjusting spring and the operating means side at the original position i.e. return-point. Therefore, an excessive load is applied to the return spring of the operating means in the original return-point. In addition, the urging force of the adjusting spring cannot be sufficiently enlarged due to the above-mentioned excessive load.
The main object of the present invention is to provide an automatic tension-regulating device for a control wire, which can be employed for a control wire without a conduit, as well as for a control cable with a conduit.
Another object of the present invention is to provide an automatic tension-adjusting device in which a connection between a control wire and an operating means side is kept even if in the return-point of the operating means, and therefore, an excessive and useless load in the return spring of the driven device can be reduced, and the urging force of the adjusting spring can be sufficiently enlarged.
Another object of the present invention is to provide an automatic tension-regulating device for a control wire, which is simplified in structure and can be securely operated.